The present invention relates to an apparatus for protecting an image pickup tube in a television camera.
In usual television camera, there is provided an auto iris control system for driving automatically an iris mechanism in such a manner that an output video signal from the camera has always a desired level even if an amount of incident light emanating from an object to be picked up fluctuates.
When the picking up operation has been finished, the iris mechanism should be driven into a fully closed condition, i.e. the minimum aperture condition or a filter having the highest density should be inserted in an optical path. If such an operation is forgotten, a photoelectric surface, e.g. a target of the pickup tube is unnecessarily irradiated by undesired light and a large amount of electrostatic charge might be stored therein. Therefore, the target might be deteriorated due to fatigue and in an extreme case, the target might be burnt. Then, it is impossible to derive the correct video signal from which an image of good quality is reproduced.
In order to avoid the above mentioned drawback, the inventor has proposed an apparatus for protecting the pickup tube in which the iris mechanism is automatically driven into the minimum aperture condition in response to a switch off of a main power supply. Usually, the television camera further comprises a manual iris control in which the iris mechanism can be manually driven by rotating an iris ring. Such a manual iris control is necessary for picking up special scenes. For instance, picking up a subject against the light and picking up a small bright subject in a dark background. In case of manual control, the iris mechanism is disconnected from an iris control circuit and thus, when the picking up operation is finished while the manual iris control has been selected, the above mentioned automatic protecting mechanism could not work, because a motor in the iris mechanism is not energized. Therefore, the iris is remained an open condition and thus, the target of the pickup tube might be damaged or deteriorated by the light impinging upon the target through the opened iris.